Code division multiple access (CDMA) communications have been used for some time. Typically, transmitted data is formatted and the spectrum is spread using CDMA spreading codes for communicating CDMA spread spectrum communication signals between a transmitter and a plurality of receivers within a null-to-null communications bandwidth. A transmitted signal includes superimposed spread spectrum signals spread by respective spreading codes for providing code division access to multiple receivers. Differing spreading codes provide signal code division multiplexing for enabling the respective receivers to acquire particular respective communication spread spectrum signals among all of the transmitted spread spectrum signals of the transmitted signal. The CDMA communication systems use a particular digital format to format a data stream prior to spectrum spreading and prior to transmission. The digital format is also applied to the spreading codes prior to spreading formatted data. One such digital format is the nonreturn to zero (NRZ) format. Another format is the Manchester format, also known as biphase-L. In an NRZ CDMA communication system, an NRZ format is used to format separate data streams into NRZ formatted data streams that are then spectrum spread by respective NRZ formatted CDMA spreading codes for transmission to respective receivers. The communication spectrum of an NRZ formatted and spread spectrum CDMA signal is characterized as having a center peak in the communications bandwidth. The communication spectrum is also referred to as a nonsplit spectrum. In a Manchester CDMA communication system, a Manchester format is used to format many separate data streams into Manchester formatted data streams that are then spectrum spread by respective Manchester formatted CDMA spreading codes for transmission to respective receivers. The communication spectrum of a Manchester formatted and spectrum spread CDMA signal is characterized as having a bandwidth center null of the communications bandwidth. This spectrum is also known as a split spectrum.
Typically, a CDMA system using NRZ formatting has a peak power spectral density at the center of the frequency band and is characterized as a nonsplit spectrum signal. A CDMA system using Manchester code formatting has a power spectral density null at the center of the frequency band and is characterized as a split spectrum signal. Another available digital format is the binary offset carrier format that also provides a split spectrum of a spread spectrum communication CDMS signal. The binary offset carrier format is a general case of the Manchester format. Conventional CDMA communication systems typically use NRZ code formatting. However, CDMA communication systems can also be implemented using a split spectrum code format, such as the Manchester code digital format and the binary offset carrier digital format.
An NRZ CDMA communication system may, for example, have an available bandwidth of 200 kHz and have a data rate of 400 bps. The spreading code chipping rate for the CDMA may be set at 100 kHz so that the null-to-null bandwidth for the spectrum spread CDMA signal is 200 kHz with a center peak. Channel capacity is the number of communication channels, that is, spread spectrum signals, which can be communicated within a given bandwidth. Using NRZ formatting, the channel capacity is about thirty-eight at a BER of 10−5. With the same signaling conditions, Manchester formatting and binary offset carrier digital formatting also provide about the same channel capacity. Channel capacity is a valuable resource. Increasing the channel capacity increases the number of users that can be served by a CDMA communication system. The NRZ, Manchester, and binary offset carrier formatted CDMA communication systems have severely limited channel capacities. These and other disadvantages are solved or reduced using the invention.